It was shown that thermal stability of finely dispersed alumina - secondary carrier of honeycomb struc-ture catalysts - increases as a result of modifying with rare-earth oxides (La2O3 and CeO2). The highest thermal stability effect for La2O3 was revealed. The reason of this effect was the formation of solid solu-tion of La2O3 in Al2O3 that hindered aluminium ion diffusion and transition of low-temperature alumina modifications into high-temperature α-Al2O3.